This invention relates generally to the control of space heating systems and more particularly, to a method of control which utilizes a plurality of electrical resistance heaters, one of which is adapted for modulated control for precise matching of heat output to a heating demand.
In known systems, it is common to energize a complete heating system whenever the actual temperature within a space to be heated falls below a set point temperature by some predetermined minimum value. It is known that thermostatic controls of this type inherently introduce a delay between that time when the actual temperature within the space rises to the set point value and the time when the thermostatic element is able to detect this increase in temperature. Similarly, the thermostatic device will typically exhibit a delay in detecting an actual temperature of which falls below the set point. The resulting overshoot and undershoot of the actual temperature versus the set point temperature may be uncomfortable to the space occupant and is wasteful of energy.
One approach to the solution of this problem is described in U.S. Pat. No. 4,379,483 which shows a method of controlling heat sources using an initial, proportional energization of a first source. If this source is unable to meet the demand for heat, it is fully energized and a second source is thereupon proportionally energized. This sequence continues until the source(s) develops sufficient heat to meet the demand. If, upon initial actuation, the actual space temperature is more than 1.5.degree. F., below the set point temperature, all heat sources are energized and maintained so until the actual temperature rises to a value which is within 1.degree. F. of the set point temperature. At this time, all heating sources are de-energized and thereupon the proportional energization sequence described above is initiated. The temperature in the space must process through a full temperature rise and decline cycle each time it is desired to transfer a heat source from proportional to fully energized control.
While such methods have heretofore been satisfactory, they tend to be characterized by certain disadvantages. In particular, they require the energization of all heat sources unless the actual space temperature is within a predetermined proximity to the set point temperature. Further, they require that the actual space temperature experience a number of cyclic excursions, either requirement of which may be uncomfortable to occupants and wasteful of energy.
A method of controlling a heating system which precisely energizes heating sources in accordance with the magnitude of the difference between the actual and set point temperatures would be a distinct advance in the art.